The present invention relates to a method for the production of a hot formed and press hardened motor vehicle body structure, and to a motor vehicle body structure.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
It is generally known to increase strength of motor vehicle structural parts, such as body structures, by using high-strength steel or super high-strength steel. This significantly increases strength and torsional stiffness even though the wall thickness remains the same and the specific weight remains substantially the same. By using this type of material, it is also conceivable to reduce the wall thickness while still attaining at least same or slightly enhanced stiffness. As a result, the specific weight of the structure decreases in the absence of any loss in strength. As weight is saved or strength is increased, the total weight of the motor vehicle can be reduced which in turn results in lower fuel consumption and accompanying CO2 emission.
Combined hot forming and press hardening has been used to produce high-strength steel or super high-strength steel. This process involves heating of a hardenable steel alloy which is then formed in the heated state and hardened through quenching. Heating is hereby executed to a temperature above austenitizing temperature or above Ac3 temperature of the respectively used steel. There are various possibilities to quench hot formed steels, with a combined hot forming and press hardening tool having been shown as especially effective. In such a tool, a flow of coolant is used to lower the temperature or to cool the hot-formed structure. Selecting cooling times and cooling rates permit adjustment of strength properties of the structure in a desired way. In addition, it is also possible to target certain regions of the structure in order to provide desired strength properties.
Body structures produced in this way require finishing or post-treatment operations, when the structure should be provided with openings, holes, feedthroughs or recesses. As press hardening results in high-strength or super high-strength properties, the provision of holes or openings becomes very difficult and machine tools used for this process are subject to high wear, causing an increase in production costs. To attain a high degree of precision in shape, it has been conventional wisdom that the formation of openings, feedthroughs, or holes in the structure prior to hot forming and press hardening should be avoided.
It would be desirable and advantageous to provide an improved method for the production of a hot formed and press hardened motor vehicle body structure to obviate prior art shortcomings.